[mman30]

I have been planning a 6 month cruise from the Chesapeake down South for the past three years. There are only a few last minute preparations before I leave at the end of Oct. One of those issues are my ice box, and prolonging my block ice. Has anyone used dry ice blocks (1 small block), along with block wet-ice, layer of cardboard(or insulating material) then properly stored food above that. My ice box does drain to the bilge, and I am aware that the dry ice gas can suck out oxygen. I am planning on rigging a pump to drain excess water out of the ice box, and overboard via a thru-hull draining grey water from galley sink.. The boat is 30', and I don't want to do anything dangerous. Any advice on using dry ice, or retrofitting a 35 year old icebox to prolong the ice. I am also aware of not opening closing to often, pack most used on top, and least used on bottom, etc. But what are the dry ice possibilities?